The development of new timepieces in recent years has largely tended to concentrate on the so called quartz type which employs a quartz crystal as time standard and in conjunction therewith may use a classic type display employing time displaying hands driven through the agency of a miniaturized electric stepping motor. The properties of such stepping motors are such that it is highly desirable to avoid that motion or forces be transmitted from the display towards the motor itself. Such transmission of force can easily come about through inertia developed when the timepiece goes through violent changes of motion or direction as is normally the case when it is worn by the user.
Although the inventor is unaware of previous employment of one-way gearing in the specific application hereinafter referred to nevertheless he acknowledges that such gearing is in itself known in various forms. For example Swiss Pat. No. 599 485 illustrates a form of one-way gearing as employed between the gear train and a calendar mechanism in a watch. Various embodiments of this particular one-way gear train have been shown, but all of them have in common that the toothing as shown occurs in two planes. Furthermore, from the description and the drawings of the aforesaid Swiss patent it will be clear that the motion as transmitted will be converted from a regular motion into a stepping motion. In a mechanism where the input itself is a stepping motion this may turn out to be highly undesirable. Furthermore, the fact that the toothing on the gears shown in the prior art occurs in two planes will complicate the manufacture thereof. Finally, such an arrangement as is shown in this particular patent will be thicker than is normally desirable should the mechanism be intended for use in small timepieces such as ladies wrist-watches.
Another specialized form of gearing is shown in French patent publication No. 2,328,140. In this case the object is to prevent rotation of a driven gear in the sense opposite to its normal sense of rotation. To obtain the desired effect the driving gear is provided with an alternating pattern of thick and thin teeth while the driven gear has portions cut away from its teeth. In such a manner rotation of the driving gear in the wrong sense is blocked when the teeth butt together between driving and driven gear. Clearly, the object of the French publication as well as the means to obtain such object are different from those of the present invention.
In the present case both driving and driven gear are mutilated in a particular manner as will be hereinafter described in order to arrive at the desired objective. The specific form of mutilation employed in the gear transmission of the present invention enables that rotational motion may be transmitted in either rotation sense from the driving gear to the driven gear. However, should a reaction take place, for instance, in the display arrangement of a wristwatch, the effect of this will not be transmitted back to the stepping drive motor since, in fact, any transmission from the driven gear to the driving gear will be blocked through butting of teeth between the two gears constituting the specific transmission.
Although it is essential for the design and functioning of the present mechanism that drive applied to the driving gear be in the form of a stepping motion, it will be clear from what will follow and what has already been said that although well adapted to the needs of watches, clocks and other instruments of the timekeeping industry the mechanism will also find employment in other arrangements and thus, the invention is not intended to be limited to timekeeping applications.